A Dual-Cam Parallel Elastic Actuator with Shared Gas-Spring Compensation for Humanoid Ankles
2026-08-31 • Robotics
Robotics
AI summaryⓘ
The authors designed a new type of actuator for humanoid robot ankles that helps with movements in two directions (pitch and roll) using just one shared spring. Their design is more compact because it uses a dual-cam mechanism to adjust torque without needing multiple springs. They also created a mathematical model to understand how the two directions affect each other and used it to optimize the actuator’s shape for specific tasks. Simulations show that their design is practical and can effectively reduce the required torque. Overall, this work offers a smaller and customizable solution to improve ankle joint assistance in robots.
2-DoF (Two Degrees of Freedom)Parallel Elastic Actuator (PEA)Torque CompensationDual-cam MechanismGas SpringMathematical ModelingOptimizationFinite Element Analysis (FEA)Humanoid RoboticsKinematic Simulation
Authors
Jingcheng Jiang, Yifang Zhang, Nikos G. Tsagarakis
Abstract
To improve torque capacity and energy efficiency of humanoid ankles, this paper proposes a 2-DoF parallel elastic actuator (PEA). The main novelty of the proposed design lies in its dual-cam, single-gas-spring architecture, which enables torque compensation in both pitch and roll using a shared elastic element, thereby improving structural compactness compared with conventional multi-element compensation schemes. By leveraging parallel gas springs and customized cam modules, the proposed architecture provides dual-axis torque assistance tailored to specific task requirements. The second key contribution is the formulation of a coupled 2-DoF mathematical model that explicitly captures the interdependence between the two compensation units through the shared spring. Based on this model, an optimization-based design framework is developed to synthesize customized cam profiles from prescribed torque references, establishing a systematic link from task requirements to hardware realization. The complete lower-leg CAD integration is presented in detail. Static FEA and kinematic simulations confirm the design's feasibility and torque-relief effectiveness. The results highlight the proposed design as a compact, customizable solution for 2-DoF humanoid ankle torque compensation.